This section is intended to provide background information to facilitate a better understanding of the various aspects of the described embodiments. Accordingly, it should be understood that these statements are to be read in this light and not as admissions of prior art.
To produce hydrocarbons (e.g., oil, gas, etc.) from a subterranean formation, wellbores may be drilled that penetrate hydrocarbon-containing portions of the subterranean formation. The portion of the subterranean formation from which hydrocarbons may be produced is commonly referred to as a “production zone.” In some instances, a subterranean formation penetrated by the wellbore may have multiple production zones at various locations along the wellbore.
Generally, after a wellbore has been drilled to a desired depth, completion operations are performed. Such completion operations may include inserting a liner or casing into the wellbore and, at times, cementing the casing or liner into place. Once the wellbore is completed as desired (lined, cased, open hole, or any other known completion), a stimulation operation may be performed to enhance hydrocarbon production into the wellbore. Examples of some common stimulation operations involve hydraulic fracturing, acidizing, fracture acidizing, and hydrajetting. Stimulation operations are intended to increase the flow of hydrocarbons from the subterranean formation surrounding the wellbore into the wellbore itself so that the hydrocarbons may then be produced up to the wellhead.
In some applications, it may be desirable to individually and selectively create multiple fractures at a predetermined distance from each other along a wellbore by creating multiple “pay zones.” In order to maximize production, these multiple fractures should have adequate conductivity. The creation of multiple pay zones is particularly advantageous when stimulating a formation from a wellbore or completing a wellbore, specifically, those wellbores that are highly deviated or horizontal. The creation of such multiple pay zones may be accomplished using a variety of tools, which may include a movable fracturing tool with perforating and fracturing capabilities or actuatable sleeve assemblies disposed in a downhole tubular.
One typical formation stimulation process may involve hydraulic fracturing of the formation and placement of a proppant in those fractures. Typically, a fracturing fluid (comprising a spacer fluid and the proppant) is mixed at the surface before being pumped downhole in order to induce fractures in the formation of interest. The creation of such fractures will increase the production of hydrocarbons by increasing the flow paths in to the wellbore.
Oftentimes well operators attempt to “pillar frack” the formation, which involves introducing pulses or plugs of proppant into the spacer fluid cyclically, thereby providing the target production zone with a step-changed fracturing fluid. In theory, the step-changed fracturing fluid creates strategically placed proppant pillars within the fractured formation, thereby enhancing conductivity. The transition from the spacer fluid to a mixture of spacer fluid and proppant is an abrupt or sharp step-change. However, conventional methods of mixing the proppant and spacer fluid often result in a spreading of the transition between the spacer fluid and the proppant, thereby leading to a gradual transition rather than the desired step-change.